Looking at the holdover tables, I would tend to concur that freezing FOG is not that problematical (usually). After all, it's just like flying through cloud above the freezing level and we do that all the time. There are set/timed procedures for shedding ice build-up on fan blades and the holdover times using the better class of fluids are not too bad compared with other forms of precipitation.
The real 'nasty' is freezing RAIN and you wouldn't catch me even attempting to taxi in that...